For an underwater oil well to become operational it is necessary to install at the well-head an assembly known as a "Christmas Tree" which combines equipment for monitoring and controlling the output flow from the well.
The Christmas Tree fitted to the well-head comprises, in particular, a large number of hydraulically actuated valves, the remote control of which is effected from a general operating station on the surface.
In particular, this operating station can be located on an oil rig which is connected to one or more underwater stations each by an umbilical cord providing the means for conveying electrical and/or hydraulic energy and the transmission of electrical or optical signals for controlling the oil extraction. The operating station may also be shore based.
Each underwater station may comprise one or more well-heads.
The operating station on the surface thus enables the remote control of a very large number of valves.
Each of the hydraulically actuated valves is of the type comprising a hydraulic valve actuator which is connected to a supply of pressurized fluid via a control unit, comprising a control valve for the flow of pressurized fluid and means for connecting the unit to the supply of pressurized fluid and to the network for transmission of control signals of the valve.
According to a known arrangement, the control of the operation of the assembly of hydraulically actuated valves of a Christmas Tree of one well-head is effected by a control unit secured to the well-head and which is connected to the hydraulic valve actuators by flexible pipes.
This control unit, which is known as a Sub-sea Control Module (SCM) or "POD", is a heavy and expensive apparatus which is specific to the configuration of a well-head.
Typically, such a unit is lowered onto the sub-sea installation using special Remotely Operated Vehicles (ROVs) and Remotely Operated Tooling (ROTs) from floating work barges or service vessels using soft landing guide wires and latching pins located on the sub-sea well installation. The weight of the control unit is typically 1.5 tons or more and requires substantial framing and counterweights on the installation to balance the loads on the well-head Christmas Tree.
The present invention is concerned with the mechanism used to releasably latch the so-called sub-sea control module, or pod to the Christmas Tree.
In a known arrangement this latching mechanism comprises a screw driven bolt-like member having a star-shaped lower end adapted to engage in a complementary shaped aperture in a pod mounting base carried by the Christmas Tree. Such a device is known as a retlock, is relatively expensive to manufacture and requires motive power to drive the rotatable screw in order to move it into and out of the locking or latching condition.
The present invention is concerned with simplifying and reducing the cost of this type of latching mechanism and making it more rapidly acting.